HA/MgO nanocrystal-based hybrid hydrogel with high mechanical strength and osteoinductive potential for bone reconstruction in diabetic rats

Multiscale metal-based nanocomposites for bone and joint disease therapies

Bone and joint diseases are debilitating conditions that can result in significant functional impairment or even permanent disability. Multiscale metal-based nanocomposites, which integrate hierarchical structures ranging from the nanoscale to the macroscale, have emerged as a promising solution to this challenge. These materials combine the unique properties of metal-based nanoparticles (MNPs), such as enzyme-like activities, stimuli responsiveness, and photothermal conversion, with advanced manufacturing techniques, such as 3D printing and biohybrid systems. The integration of MNPs within polymer or ceramic matrices offers a degree of control over the mechanical strength, antimicrobial efficacy, and the manner of drug delivery, whilst concomitantly promoting the processes of osteogenesis and chondrogenesis. This review highlights breakthroughs in stimulus-responsive MNPs (e.g., photo-, magnetically-, or pH-activated systems) for on-demand therapy and their integration with biocomposite hybrids containing cells or extracellular vesicles to mimic the native tissue microenvironment. The applications of these composites are extensive, ranging from bone defects, infections, tumors, to degenerative joint diseases. The review emphasizes the enhanced load-bearing capacity, bioactivity, and tissue integration that can be achieved through hierarchical designs. Notwithstanding the potential of these applications, significant barriers to progress persist, including challenges related to long-term biocompatibility, regulatory hurdles, and scalable manufacturing. Finally, we propose future directions, including machine learning-guided design and patient-specific biomanufacturing to accelerate clinical translation. Multiscale metal-based nanocomposites, which bridge nanoscale innovations with macroscale functionality, are a revolutionary force in the field of biomedical engineering, providing personalized regenerative solutions for bone and joint diseases.

Hydrogel promotes bone regeneration through various mechanisms: a review

Large defects in bone tissue due to trauma, tumors, or developmental abnormalities usually require surgical treatment for repair. Numerous studies have shown that current bone repair and regeneration treatments have certain complications and limitations. With the in-depth understanding of bone regeneration mechanisms and biological tissue materials, a variety of materials with desirable physicochemical properties and biological functions have emerged in the field of bone regeneration in recent years. Among them, hydrogels have been widely used in bone regeneration research due to their biocompatibility, unique swelling properties, and ease of fabrication. In this paper, the development and classification of hydrogels were introduced, and the mechanism of hydrogels in promoting bone regeneration was described in detail, including the promotion of bone marrow mesenchymal stem cell differentiation, the promotion of angiogenesis, the enhancement of the activity of bone morphogenetic proteins, and the regulation of the microenvironment of bone regeneration tissues. In addition, the future research direction of hydrogel in bone tissue engineering was discussed.

Bioactive hydrogel formulations for regeneration of pathological bone defects

Bone defects caused by osteoporosis, infection, diabetes, post-tumor resection, and nonunion often cause severe pain and markedly increase morbidity and mortality, which remain a significant challenge for orthopedic surgeons. The precise local treatments for these pathological complications are essential to avoid poor or failed bone repair. Hydrogel formulations serve as injectable innovative platforms that overcome microenvironmental obstacles and as delivery systems for controlled release of various bioactive substances to bone defects in a targeted manner. Additionally, hydrogel formulations can be tailored for specific mechanical strengths and degradation profiles by adjusting their physical and chemical properties, which are crucial for prolonged drug retention and effective bone repair. This review summarizes recent advances in bioactive hydrogel formulations as three-dimensional scaffolds that support cell proliferation and differentiation. It also highlights their role as smart drug-delivery systems with capable of continuously releasing antibacterial agents, anti-inflammatory drugs, chemotherapeutic agents, and osteogenesis-related factors to enhance bone regeneration in pathological areas. Furthermore, the limitations of hydrogel formulations in pathological bone repair are discussed, and future development directions are proposed, which is expected to pave the way for the repair of pathological bone defects.

Versatile application of magnesium-related bone implants in the treatment of bone defects

Magnesium-related bone implants have garnered significant attention in the treatment of bone defects. The applications of magnesium in promoting bone repair mainly include degradable magnesium-based scaffolds owing to its special physical properties and composite materials modified by magnesium ions because of its biological activity. Although numerous studies have confirmed the unique application advantages and efficacy of magnesium in promoting bone repair, some obvious shortcomings persist, including the rapid degradation of magnesium-based scaffolds. In this review, the deficiencies of magnesium and its alloys in the construction of orthopedic implants and their key influencing factors were summarized; furthermore, some advanced improvement schemes were summarized and analyzed. Additionally, the application strategies of magnesium-modified bone implants are summarized and discussed. Lastly, this review incorporates the latest research and discoveries on magnesium in orthopedic science, comprehensively exploring the mechanism of magnesium's role in the complex microenvironment of bone defects from multiple dimensions. This paper provides a comprehensive summary and analysis of cutting-edge concepts in the design and development of magnesium-based bone implants, considering various perspectives such as the physical properties and biological functions of magnesium.

Multifaceted role of nanocomposite hydrogels in diabetic wound healing: enhanced biomedical applications and detailed molecular mechanisms

The complex microenvironment of diabetic wounds, which is characterized by persistent hyperglycemia, excessive inflammatory responses, and hypoxic conditions, significantly impedes the efficacy of traditional hydrogels. Nanocomposite hydrogels, which combine the high-water content and biocompatibility of hydrogels with the unique functionalities of nanomaterials, offer a promising solution. These hydrogels exhibit enhanced antibacterial, antioxidant, and drug-release properties. Incorporating nanomaterials increases the mechanical strength and bioactivity of hydrogels, allowing for dynamic regulation of the wound microenvironment and promoting cell migration, proliferation, and angiogenesis, thereby accelerating wound healing. This review provides a comprehensive overview of the latest advances in nanocomposite hydrogels for diabetic wound treatment and discusses their advantages and molecular mechanisms at various healing stages. The study aims to provide a theoretical foundation and practical guidance for future research and clinical applications. Furthermore, it highlights the challenges related to the mechanical durability, antimicrobial performance, resistance issues, and interactions with the cellular environments of these hydrogels. Future directions include optimizing smart drug delivery systems and personalized medical approaches to enhance the clinical applicability of nanocomposite hydrogels.

Development and characterization of novel magnesium oxide nanoparticle-impregnated chitosan-based guided tissue regeneration membrane - An in vitro study

Introduction

Although a lot of commercially available guided tissue regeneration (GTR) membranes are used, none of them could actually ensure complete bone regeneration so far and they also have certain limitations. This study aims to explore further and develop a membrane that might overcome these limitations and aid in bone regeneration for the treatment of bony defects.

Materials and Methods

Magnesium oxide nanoparticles (MgONPs) were prepared from magnesium nitrate prepared by calcination at different temperatures and dried using filter paper under specific temperature. Later, 0.3 ml of 0.2 M 1% acetic acid was added to water and placed in the stirrer for at least 1 h. Chitosan (CS) (2%) of two different concentrations containing 0.588 g and 0.576 g of CS, respectively, was prepared and added to the previous mixture. To these concentrations, the prepared MgONPs were added and stirred using a magnetic stirrer for 1 h. Later, it was cast in the mold and dried. The prepared membrane was immersed in 1 M sodium hydroxide to neutralize acetic acid. After preparation, they were subjected to scanning electron microscope (SEM) analysis, energy-dispersive X-ray (EDAX), Fourier transform infrared spectroscopy (FTIR), and contact angle test.

Results

In SEM analysis, spherical in size, uniformly dense, and porous agglomeration was noticed. EDAX and FTIR revealed the formation of MgONPs (magnesium oxide) in the membrane. The average contact angles of the CS with MgONPs and control membranes were 85.48° and 80.80°, respectively. Degradation analysis showed that test membrane showed a slower degradation rate than control collagen membrane at the end of the 28th day.

Conclusion

On comparing membranes with pure CS, membranes with nanoparticles, and control collagen membranes, the membrane incorporated with nanoparticles showed more favorable positive outcomes.

Macrophage-Centric Biomaterials for Bone Regeneration in Diabetes Mellitus: Contemporary Advancements, Challenges, and Future Trajectories

Increased susceptibility to bone fragility and the diminution of bone regenerative capacity are recognized as significant and frequent sequelae of diabetes mellitus. Research has elucidated the pivotal role of macrophages in the pathogenesis and repair of diabetic bone defects. Notwithstanding this, the therapeutic efficacy of traditional interventions remains predominantly inadequate. Concomitant with substantial advancements in tissue engineering in recent epochs, there has been an escalation in the development of biomaterials designed to modulate macrophage activity, thereby augmenting osseous tissue regeneration in the context of hyperglycemia. This review amalgamates insights from extant research and delineates recent progressions in the domain of biomaterials that target macrophages for the regeneration of diabetic bone, whilst also addressing the clinical challenges and envisaging future directions within this field.

Dynamic Cross-Linking, Self-Healing, Antibacterial Hydrogel for Regenerating Irregular Cranial Bone Defects

Given the widespread clinical demand, addressing irregular cranial bone defects poses a significant challenge following surgical procedures and traumatic events. In situ-formed injectable hydrogels are attractive for irregular bone defects due to their ease of administration and the ability to incorporate ceramics, ions, and proteins into the hydrogel. In this study, a multifunctional hydrogel composed of oxidized sodium alginate (OSA)-grafted dopamine (DO), carboxymethyl chitosan (CMCS), calcium ions (Ca2+), nanohydroxyapatite (nHA), and magnesium oxide (MgO) (DOCMCHM) was prepared to address irregular cranial bone defects via dynamic Schiff base and chelation reactions. DOCMCHM hydrogel exhibits strong adhesion to wet tissues, self-healing properties, and antibacterial characteristics. Biological evaluations indicate that DOCMCHM hydrogel has good biocompatibility, in vivo degradability, and the ability to promote cell proliferation. Importantly, DOCMCHM hydrogel, containing MgO, promotes the expression of osteogenic protein markers COL-1, OCN, and RUNX2, and stimulates the formation of new blood vessels by upregulating CD31. This study could provide meaningful insights into ion therapy for the repair of cranial bone defects.

Macrophage-mediated fracture healing: Unraveling molecular mechanisms and therapeutic implications using hydrogel-based interventions

Fracture healing is a complex biological process that involves the orchestrated interplay of various cells and molecular signaling pathways. Among the key players, macrophages have emerged as critical regulators of fracture repair, influencing inflammation, tissue remodeling, and angiogenesis. Recent advances in hydrogel-based therapeutics have provided exciting opportunities to leverage the modulatory effects of macrophages for improving fracture healing outcomes. In the present study, we review the importance of macrophages in fracture repair and their potential therapeutic role in hydrogel-based interventions. We discuss the molecular mechanisms underlying macrophage-mediated effects on fracture healing, and how hydrogels can be utilized as a platform for macrophage modulation. Furthermore, we highlight the translation of hydrogel-based therapies from bench to bedside, including preclinical and clinical studies, and the challenges and opportunities in harnessing the therapeutic potential of macrophages in fracture repair. Overall, understanding the importance of macrophages in fracture healing and the potential of hydrogel-based therapeutics to modulate macrophage responses can pave the way for developing innovative approaches to improve fracture healing outcomes.

Osteogenic Potential of Magnesium Oxide Nanoparticles in Bone Regeneration: A Systematic Review

Guided bone regeneration (GBR) plays a crucial role in the augmentation of alveolar bone, especially in cases of dental implants. The main principle behind using membranes in guided tissue regeneration (GTR) is to prevent epithelial downgrowth as well as connective tissue on the root surface. However, the membranes lack some major properties, such as osteogenic and antimicrobial properties. Magnesium (Mg) is one of the biodegradable materials that is gaining interest because of its favourable mechanical properties and biocompatibility. It also possesses pro-osteogenic properties and significant inhibition of biofilm formation and maturation. These features have attracted increasing interest in using magnesium oxide nanoparticles in GBR membrane applications. This systematic review assesses the osteogenic potential of magnesium oxide nanoparticles in periodontal bone regeneration. The literature search used PubMed, PubMed Central, Medline, and Cochrane databases to examine systematic reviews published till March 2023. Seven articles were included based on the selection criteria. We included all in vitro and in vivo clinical studies based on the osteogenic potential of magnesium oxide nanoparticles in periodontal bone regeneration. The seven studies provided evidence that magnesium oxide nanoparticles, when incorporated in any substrate, showed higher osteogenic potential in terms of higher alkaline phosphatase levels, bone volume fraction, and bone mineral density. The optimum concentration of magnesium oxide can be an ideal additive to various substrates to promote bone regeneration. Because most of the studies were conducted on calvarial defects, further studies should focus only on bone regeneration related to periodontal regeneration.

Recent advances in composite hydrogels: synthesis, classification, and application in the treatment of bone defects

Bone defects are often difficult to treat due to their complexity and specificity, and therefore pose a serious threat to human life and health. Currently, the clinical treatment of bone defects is mainly surgical. However, this treatment is often more harmful to patients and there is a potential risk of rejection and infection. Hydrogels have a unique three-dimensional structure that can accommodate a variety of materials, including particles, polymers and small molecules, making them ideal for treating bone defects. Therefore, emerging composite hydrogels are considered one of the most promising candidates for the treatment of bone defects. This review describes the use of different types of composite hydrogel in the treatment of bone defects. We present the basic concepts of hydrogels, different preparation techniques (including chemical and physical crosslinking), and the clinical requirements for hydrogels used to treat bone defects. In addition, a review of numerous promising designs of different types of hydrogel doped with different materials (e.g., nanoparticles, polymers, carbon materials, drugs, and active factors) is also highlighted. Finally, the current challenges and prospects of composite hydrogels for the treatment of bone defects are presented. This review will stimulate research efforts in this field and promote the application of new methods and innovative ideas in the clinical field of composite hydrogels.

Crosslinking strategies for biomimetic hydrogels in bone tissue engineering

Bone tissue engineering has become a popular area of study for making biomimetic hydrogels to treat bone diseases. In this work, we looked at biocompatible hydrogels that can be injected into bone defects that require the smallest possible surgery. Mineral ions can be attached to polymer chains to make useful hydrogels that help bones heal faster. These ions are very important for the balance of the body. In the chemically-triggered sector, advanced hydrogels cross-linked by different molecular agents have many advantages, such as being selective, able to form gels, and having mechanical properties that can be modified. In addition, different photo-initiators can be used to make photo cross linkable hydrogels react quickly and moderately under certain light bands. Enzyme-triggered hydrogels are another type of hydrogel that can be used to repair bone tissue because they are biocompatible and gel quickly. We also look at some of the important factors mentioned above that could change how well bone tissue engineering works as a therapy. Finally, this review summarizes the problems that still need to be solved to make clinically relevant hydrogels.

Hydrogel Tissue Bioengineered Scaffolds in Bone Repair: A Review

Large bone defects due to trauma, infections, and tumors are difficult to heal spontaneously by the body's repair mechanisms and have become a major hindrance to people's daily lives and economic development. However, autologous and allogeneic bone grafts, with their lack of donors, more invasive surgery, immune rejection, and potential viral transmission, hinder the development of bone repair. Hydrogel tissue bioengineered scaffolds have gained widespread attention in the field of bone repair due to their good biocompatibility and three-dimensional network structure that facilitates cell adhesion and proliferation. In addition, loading natural products with nanoparticles and incorporating them into hydrogel tissue bioengineered scaffolds is one of the most effective strategies to promote bone repair due to the good bioactivity and limitations of natural products. Therefore, this paper presents a brief review of the application of hydrogels with different gel-forming properties, hydrogels with different matrices, and nanoparticle-loaded natural products loaded and incorporated into hydrogels for bone defect repair in recent years.

In Vitro and In Vivo Applications of Magnesium-Enriched Biomaterials for Vascularized Osteogenesis in Bone Tissue Engineering: A Review of Literature

Bone is a highly vascularized tissue, and the ability of magnesium (Mg) to promote osteogenesis and angiogenesis has been widely studied. The aim of bone tissue engineering is to repair bone tissue defects and restore its normal function. Various Mg-enriched materials that can promote angiogenesis and osteogenesis have been made. Here, we introduce several types of orthopedic clinical uses of Mg; recent advances in the study of metal materials releasing Mg ions (pure Mg, Mg alloy, coated Mg, Mg-rich composite, ceramic, and hydrogel) are reviewed. Most studies suggest that Mg can enhance vascularized osteogenesis in bone defect areas. Additionally, we summarized some research on the mechanisms related to vascularized osteogenesis. In addition, the experimental strategies for the research of Mg-enriched materials in the future are put forward, in which clarifying the specific mechanism of promoting angiogenesis is the crux.

Drug-Delivery Nanoplatform with Synergistic Regulation of Angiogenesis-Osteogenesis Coupling for Promoting Vascularized Bone Regeneration

It has been confirmed that substantial vascularization is an effective strategy to heal large-scale bone defects in the field of bone tissue engineering. The local application of deferoxamine (DFO) is among the most common and effective methods for promoting the formation of blood vessels, although its short half-life in plasma, rapid clearance, and poor biocompatibility limit its therapeutic suitability. Herein, zeolitic imidazolate framework-8 (ZIF-8) was selected as a vehicle to extend the half-life of DFO. In the present study, a nano DFO-loaded ZIF-8 (DFO@ZIF-8) drug delivery system was established to promote angiogenesis-osteogenesis coupling. The nanoparticles were characterized, and their drug loading efficiency was examined to confirm the successful synthesis of nano DFO@ZIF-8. Additionally, due to the sustained release of DFO and Zn²⁺, DFO@ZIF-8 NPs were able to promote angiogenesis in human umbilical vein endothelial cells (HUVECs) culture and osteogenesis in bone marrow stem cells (BMSCs) in vitro. Furthermore, the DFO@ZIF-8 NPs promoted vascularization by enhancing the expression of type H vessels and a vascular network. The DFO@ZIF-8 NPs promoted bone regeneration in vivo by increasing the expression of OCN and BMP-2. RNA sequencing analysis revealed that the PI3K-AKT-MMP-2/9 and HIF-1α pathways were upregulated by DFO@ZIF-8 NPs in HUVECs, ultimately leading to the formation of new blood vessels. In addition, the mechanism by which DFO@ZIF-8 NPs promoted bone regeneration was potentially related to the synergistic effect of angiogenesis-osteogenesis coupling and Zn²⁺-mediation of the MAPK pathway. Taken together, DFO@ZIF-8 NPs, which were demonstrated to have low cytotoxicity and excellent coupling of angiogenesis and osteogenesis, represent a promising strategy for the reconstruction of critical-sized bone defects.

One-Pot Facile Encapsulation of Dimethyloxallyl Glycine by Nanoscale Zeolitic Imidazolate Frameworks-8 for Enhancing Vascularized Bone Regeneration

In the process of bone tissue regeneration, regulation of osteogenesis-angiogenesis coupling is of great importance. Therefore, dimethyloxallyl glycine (DMOG) is loaded by nanoscale zeolitic imidazolate frameworks-8 (ZIF-8) to obtain a drug-loading system that can promote osteogenesis-angiogenesis coupling. Characterization of the drug-loading nanoparticles (DMOG@ZIF-8) reveals that DMOG is successfully loaded into ZIF-8 by two different methods, and the DMOG@ZIF-8 is prepared using the one-pot method (OD@ZIF-8) achieves higher loading efficiency and longer release time than those prepared using the post-loading method (PD@ZIF-8). In vitro studies found that DMOG@ZIF-8 significantly enhances the migration, tube formation, and angiogenesis-related protein secretion of human umbilical vein endothelial cells as well as the extracellular matrix mineralization, alkaline phosphatase activity, and osteogenesis-related protein secretion of bone marrow mesenchymal stem cells. Moreover, OD@ZIF-8 nanoparticles are more efficient than PD@ZIF-8 nanoparticles in induction of osteogenesis-angiogenesis coupling. Then, in vivo cranial critical defect model shows that the addition of OD@ZIF-8 significantly promotes vascularized bone formation as indicated by the results including microcomputed tomographic, histological and immunofluorescence staining, and so on. Taken together, loading ZIF-8 with DMOG may be a promising solution for critical-sized bone defect reconstruction and the one-pot method is preferred in the preparation of such drug-loading system.

Porous hydroxyapatite scaffold orchestrated with bioactive coatings for rapid bone repair

Current bioceramic scaffolds for critical-size bone defects are still facing various challenges such as the poor capability of self-resorption, vascularization and osteogenesis. Herein, a composite scaffold (HOD) is fabricated by integrating bioactive coatings of konjac glucomannan (KGM) and deferoxamine (DFO) into porous hydroxyapatite scaffold (HA), where KGM coating induces the self-resorption of HOD after implanting and DFO promoted the vascularization at the defected bone. Porous HA scaffolds with 200-400 μm of pore sizes were prepared and these bioactive coatings were successfully deposited on the scaffold, which was confirmed by SEM. MC3T3-E1 cells could be tightly attached to the pore wall of HOD and the obvious osteogenic differentiation was clearly displayed after 14 days of co-culture. Besides, HOD displayed the potential of promoting the vascularization of HUVECs. Importantly, the accelerated degradation of HOD was observed in a macrophage-associated acidic medium, which led to the self-resorption of HOD in vivo. Micro-CT images showed that HOD was gradually replaced by newly formed bone, achieving a balance between the new bone formation and the scaffold degradation. The rapid bone repairing of the femoral defects in rats was displayed for HOD in comparison to the HA scaffold. Moreover, the therapeutic mechanism of HOD was highly associated with promoted osteogenesis and vascularization. Collectively, the porous ceramic scaffold orchestrated with bioactive coatings may be a promising strategy for repairing of the large bone defect.

Dysfunction of macrophages leads to diabetic bone regeneration deficiency

Insufficient bone matrix formation caused by diabetic chronic inflammation can result in bone nonunion, which is perceived as a worldwide epidemic, with a substantial socioeconomic and public health burden. Macrophages in microenvironment orchestrate the inflammation and launch the process of bone remodeling and repair, but aberrant activation of macrophages can drive drastic inflammatory responses during diabetic bone regeneration. In diabetes mellitus, the proliferation of resident macrophages in bone microenvironment is limited, while enhanced myeloid differentiation of hematopoietic stem cells (HSCs) leads to increased and constant monocyte recruitment and thus macrophages shift toward the classic pro-inflammatory phenotype, which leads to the deficiency of bone regeneration. In this review, we systematically summarized the anomalous origin of macrophages under diabetic conditions. Moreover, we evaluated the deficit of pro-regeneration macrophages in the diabetic inflammatory microenvironment. Finally, we further discussed the latest developments on strategies based on targeting macrophages to promote diabetic bone regeneration. Briefly, this review aimed to provide a basis for modulating the biological functions of macrophages to accelerate bone regeneration and rescue diabetic fracture healing in the future.

Controlled magnesium ion delivery system for in situ bone tissue engineering

Magnesium cation (Mg²⁺) has been an emerging therapeutic agent for inducing vascularized bone regeneration. However, the therapeutic effects of current magnesium (Mg) -containing biomaterials are controversial due to the concentration- and stage-dependent behavior of Mg²⁺. Here, we first provide an overview of biochemical mechanism of Mg²⁺ in various concentrations and suggest that 2-10 mM Mg²⁺in vitro may be optimized. This review systematically summarizes and discusses several types of controlled Mg²⁺ delivery systems based on polymer-Mg composite scaffolds and Mg-containing hydrogels, as well as their design philosophy and several parameters that regulate Mg²⁺ release. Given that the continuous supply of Mg²⁺ may prevent biomineral deposition in the later stage of bone regeneration and maturation, we highlight the controlled delivery of Mg²⁺ based dual- or multi-ions system, especially for the hierarchical therapeutic ion release system, which shows enhanced biomineralization. Finally, the remaining challenges and perspectives of Mg-containing biomaterials for future in situ bone tissue engineering are discussed as well.

Electrospun hydroxyapatite loaded L-polylactic acid aligned nanofibrous membrane patch for rotator cuff repair

Rotator cuff repair remains a challenge clinically due to the high retear rate after surgical intervention. There is a significant need to develop functional biomaterials facilitating tendon-to-bone integration. In this study, hydroxyapatite (HA) incorporated polylactic acid (PLLA) aligned nanofibrous membranes were fabricated by electrospinning as a low-cost sustainable rotator cuff patch. The morphology, physical, mechanical and in vitro cell assays of the nanofibrous membranes were characterized. The results showed that the nanofibrous membrane maintained a rough surface and weakened hydrophobicity. It has excellent cytocompatibility, and the cells were oriented along the direction of fiber arrangement. What's more, the PLLA-HA nanofibrous membrane could increase the alkaline phosphatase (ALP) expression in rat bone marrow mesenchymal stem cells (BMSCs), indicating that the electrospinning PLLA-HA nanofibrous membrane can better induce the bone formation of rat BMSCs cells. When the mass ratio of PLLA to HA exceeds 3: 1, with the increase of the HA content, the patch showed rising induction ability. The results suggested that electrospinning PLLA-HA nanofibrous membranes are an ideal patch for promoting tendon-bone healing and reducing the secondary tear rate. Furthermore, the use of biodegradable polymers and low-cost preparation methods presented the possibility for commercial production of these nanofibrous membranes.

Fabrication of physical and chemical crosslinked hydrogels for bone tissue engineering

Bone tissue engineering has emerged as a significant research area that provides promising novel tools for the preparation of biomimetic hydrogels applied in bone-related diseases (e.g., bone defects, cartilage damage, osteoarthritis, etc.). Herein, thermal sensitive polymers (e.g., PNIPAAm, Soluplus, etc.) were introduced into main chains to fabricate biomimetic hydrogels with injectability and compatibility for those bone defect need minimally invasive surgery. Mineral ions (e.g., calcium, copper, zinc, and magnesium), as an indispensable role in maintaining the balance of the organism, were linked with polymer chains to form functional hydrogels for accelerating bone regeneration. In the chemically triggered hydrogel section, advanced hydrogels crosslinked by different molecular agents (e.g., genipin, dopamine, caffeic acid, and tannic acid) possess many advantages, including extensive selectivity, rapid gel-forming capacity and tunable mechanical property. Additionally, photo crosslinking hydrogel with rapid response and mild condition can be triggered by different photoinitiators (e.g., I2959, LAP, eosin Y, riboflavin, etc.) under specific wavelength of light. Moreover, enzyme triggered hydrogels were also utilized in the tissue regeneration due to its rapid gel-forming capacity and excellent biocompatibility. Particularly, some key factors that can determine the therapy effect for bone tissue engineering were also mentioned. Finally, brief summaries and remaining issues on how to properly design clinical-oriented hydrogels were provided in this review.

Strategies for interface issues and challenges of neural electrodes

Neural electrodes, as a bridge for bidirectional communication between the body and external devices, are crucial means for detecting and controlling nerve activity. The electrodes play a vital role in monitoring the state of neural systems or influencing it to treat disease or restore functions. To achieve high-resolution, safe and long-term stable nerve recording and stimulation, a neural electrode with excellent electrochemical performance (e.g., impedance, charge storage capacity, charge injection limit), and good biocompatibility and stability is required. Here, the charge transfer process in the tissues, the electrode-tissue interfaces and the electrode materials are discussed respectively. Subsequently, the latest research methods and strategies for improving the electrochemical performance and biocompatibility of neural electrodes are reviewed. Finally, the challenges in the development of neural electrodes are proposed. It is expected that the development of neural electrodes will offer new opportunities for the evolution of neural prosthesis, bioelectronic medicine, brain science, and so on.

Magnesium Oxide Nanoparticle Coordinated Phosphate-Functionalized Chitosan Injectable Hydrogel for Osteogenesis and Angiogenesis in Bone Regeneration

Natural polysaccharide (NPH)-based injectable hydrogels have shown great potential for critical-sized bone defect repair. However, their osteogenic, angiogenic, and mechanical properties are insufficient. Here, MgO nanoparticles (NPs) were incorporated into a newly synthesized water-soluble phosphocreatine-functionalized chitosan (CSMP) water solution to form an injectable hydrogel (CSMP-MgO) via supramolecular combination between phosphate groups in CSMP and magnesium in MgO NPs to circumvent these drawbacks of chitosan-based injectable hydrogels. Water-soluble chitosan deviate CSMP was first synthesized by grafting methacrylic anhydride and phosphocreatine into a chitosan chain in a one-step lyophilization process. The phosphocreatine in this hydrogel not only provides sites to combine with MgO NPs to form supramolecular binding but also serves as the reservoir to control Mg2+ release. As a result, the lyophilized CSMP-MgO hydrogels presented a porous structure with some small holes in the pore wall, and the pore diameters ranged from 50 to 100 μm. The CSMP-MgO injectable hydrogels were restricted from swelling in DI water (lowest swelling ratio was 16.0 ± 1.1 g/g) and presented no brittle failure during compression even at a strain above 85% (maximum compressive strength was 195.0 kPa) versus the control groups (28.0 and 41.3 kPa for CSMP and CSMP-MgO (0.5) hydrogels), with regulated Mg2+ release in a stable and sustained manner. The CSMP-MgO injectable hydrogels promoted in vitro calcium phosphate (hydroxyapatite (HA) and tetracalcium phosphate (TTCP)) deposition in supersaturated calcium phosphate solution and presented no cytotoxicity to MC3T3-E1 cells; the CSMP-MgO hydrogel promoted MC3T3-E1 cell osteogenic differentiation with upregulation of BSP, OPN, and Osterix osteogenic gene expression and mineralization and HUVEC tube formation. Among them, CSMP-MgO (5) presented most of these properties. Moreover, this hydrogel (CSMP-MgO (5)) showed an excellent ability to promote new bone formation in critical-sized calvarial defects in rats. Thus, the CSMP-MgO injectable hydrogel shows great promise for bone regeneration.

A review of recent advances in metal ion hydrogels: mechanism, properties and their biological applications

The mechanisms, common properties and biological applications of different types of metal ion hydrogels are summarized.

Clay-based nanocomposite hydrogel with attractive mechanical properties and sustained bioactive ion release for bone defect repair

Although clay-based nanocomposite hydrogels have been widely explored, their instability in hot water and saline solution inhibits their applications in biomedical engineering, and the exploration of clay-based nanocomposite hydrogels in bone defect repair is even less. In this work, we developed a stable clay-based nanocomposite hydrogel using 4-acryloylmorpholine as the monomer. After UV light illumination, the obtained poly(4-acryloylmorpholine) clay-based nanocomposite hydrogel (poly(4-acry)-clay nanocomposite hydrogel) exhibits excellent mechanical properties due to the hydrogen bond interactions between the poly(4-acryloylmorpholine) chains and the physical crosslinking effect of the nanoclay. Besides good biocompatibility, the sustainable release of intrinsic Mg2+ and Si4+ from the poly(4-acry)-clay nanocomposite hydrogel endows the system with excellent ability to promote the osteogenic differentiation of primary rat osteoblasts (ROBs) and can promote new bone formation effectively after implantation. We anticipate that these kinds of clay-based nanocomposite hydrogels with sustained release of bioactive ions will open a new avenue for the development of novel biomaterials for bone regeneration.